Maybe I dont need the X. I have a 12.5-1, 499 ci. 275 @ .50 and .660 Lift solid roler cam, 8" 5000 rpm converter, 28" tire and 3.73 gears. I was trapping befor at around 6300 rpm. I would assume i should be around the 6500 maybe + a little with the new setup. Prob wont be reving higher then 7000. car weighs 3750 with me in it. Currently runs 10.60's with the stage VI heads and am hoping these TF 270's willadd a little power over my stage Vi's